Production of polyvinyl alcohol fibers characterized by improved dyeability and elasticity



United States PateiitO 3,071,429 PRODUCTION OF POLYVINYL ALCOHOL FIBERS CHARACTERIZED BY IMPROVED DYEABILITY AND ELASTICITY Yasuji Ohno, Hitoshi Abe, and Kenichi Tanabe, Kurashiki City, Japan, assignors of three-fourths to Kurashiki Rayon (30., Ltd, Okayama, Japan, a corporation of Japan, and one-fourth to Air Reduction Company IncYoi-plgrated, New York, N.Y., a corporation of New or No Drawing. Filed June 2, 1959, Ser. No. 817,458 Claims priority, application Japan June 9, 1958 5 (Ilaims. (Cl. 8-1155) This invention relates to a method of improving the properties of shaped polyvinyl alcohol bodies, particularly of fibers of the polyvinyl alcohol series. It relates especially to a method of improving the dyeing characteristics of such fibers, as well as giving good elasticity.

It is known that polyvinyl alcohol fibers, as produced by a wet or dry spinning of polyvinyl alcohol solutions, generally are subjected to an after-treatment to obtain the properties necessary for use as all-purpose textile fibers. The best known after-treatment is the acetalization with formaldehyde or acetaldehyde, which is employed to increase the Water resistance of the fibers. This acetalization treatment may be preceded by a heat treatment to improve the softening temperature in water. Although these procedures impart to polyvinyl alcohol fibers improved water resistance the acetalized fibers thus obtained have inferior dyeing properties and low elasticity.

Superior elasticity at low degrees of elongation results on treating polyvinyl alcohol fibers with aliphatic aldehydes having several carbon atoms. Good elastic re covery, as Well as good dry and wet heat resistance, can be obtained by subjecting polyvinyl alcohol fibers to heat treatment and then to acetalization with aromatic aldehydes, or substituted aromatic aldehydes, wherein the aldehyde radical is directly bonded to a carbon atom on an aromatic nucleus, or with cyclic aldehydes or aliphatic aldehydes containing an aromatic substituent.

Various procedures have been undertaken to improve the dyeability of such fibers, as well as to improve the dyeing method. So called animalization methods have been satisfactory. In these procedures the fibers are treated with substances such as amino-substituted aldehydes which introduce a basic amino group on the fiber and thus gives greatly increased susceptibility of the fiber to acid dyes.

Although improved dyeing characteristics or improved elasticity can be achieved separately by the above processes, it is generally difiicult to achieve an improvement in both the dyeability and elasticity simultaneously. Carrying out both the animalization, and theacetalization with higher molecular weight aldehydes; simultaneously usually results in only a partial achievement of purpose. In fact, production of a high elasticity by acetalization tends to have a deleterious effect on the dyeing characteristics. Conversely, production of good dyeability may obstruct acetalization with the higher molecular weight aldehydes, resulting in a sacrifice of elasticity.

A principal object of this invention is to provide a method for treating polyvinyl alcohol fibers which will produce improved dyeing characteristics and at the same time give improved elasticity.

Another object of the invention is to provide a polyvinyl alcohol fiber having improved physical characteristics and being suitable as a synthetic fiberfor the manufacture of textiles. I

Other objects and advantages of the invention will be apparent from a consideration of the specification and claims. 1 l

3,071,429 Patented Jan. 1,- 1963 ice The present invention is based upon the discovery that polyvinyl alcohol fibers having good dyeability, and at the same time improved elasticity, may be obtained by treating the polyvinyl alcohol fiber first with a cyanosubs'tituted aromatic or cyclic aliphatic aldehyde and then with hydroxylamine.

Treatment of a polyvinyl alcohol fiber with a cyanosubstituted aromatic or cyclic aliphatic aldehyde alone is known to improve the elasticity of the fiber. However, such treated fiber has poor affinity to dyestuflr'. It will not be satisfactorily stained with direct acid dyestuffs. After treament of the fibers aceltalized in thismanner with hydroxylamine, however, the aflinity of the fiber for acid and direct dyestuffs will be greatly increased, the greater part of the dyestuif being absorbed. Moreover, the elasticity will remain good after the hydroxylamine treat: ment; vthere is no noticeable qualitativedeterioration in elasticity. This was not to be expected in view of the fact that in cases where acetalization with the higher molecular weight aldehyde is followed by the conventional aminoacetalization treatments, the dyeing character of the fiber deteriorates. I

The explanation appears to be that the hydroxylamine reacts with the cyano groups which have already been introduced into the fiber by the previous acetalization process, probably according to the following reaction:

compounds: 0-, m-, and p-cyanobenzaldehydes, p-(cyanomethyl)benzaldehyde, o (B cyanoethyDbenzaldehyde,

'2-chloro-4-cyano-, and 3-bromo-5-cyanobenzaldehyde, 3-

cyanoand 4 cyano 1,2,5,6 tetrahydrobenzaldehyde, 3-cyano-1,2,3,6-tetrahydrobenzaldehyde', 4 cyanohexahydrobenzaldehyde and cyanonaphthaldehyde, Also included are compounds hydrolyzable into such aldehydes in situ, i.e. aldehyde precursors such as acetals.

The degree of acetalization with the cyano-substituted aldehyde must be at least 5%, i.e. at least 5% of the original hydroxyl groups present in the fiber must be acetalized by the aldehyde treatment. If the degree of .acetalization is less than this amount, the dyeing characteristics of the fiber after subsequent treatment with 'hydroxylamine will not be satisfactory.

When the less soluble cyano-substituted aldehydes are used, acetalization of the polyvinyl alcohol fiber can be performed satisfactorily with such aldehydes in aqueous medium with the addition of surface active agents.

It is known that acetalization with formaldehyde irnproves the heat and wet heat resistance of polyvinyl a1- :cohol articles, whereas acetalization with the higher and water repellency. Therefore, amodification of our invention consists in combining the two acetalization v procedures so as to obtain a polyvinyl alcohol article cyano-substituted aldehydes improves the elastic recovery having a high softening point in air and water, as .well as goodelastic properties and Water repellency.. This f"ca n'be accomplished by using a single acetalization bath containing formaldehyde and a cyano-substituted aldehyde, or by subjecting the article to successive treatments, in any order.

In the first step of the process, namely acetalization with the cyano-substituted aldehyde, the polyvinyl alcohol fiber is treated in an aqueous solution or dispersion usually containing 0.2 to 10% (preferably 25%) of the aldehyde, 0.2 to 30% (preferably 3-l0%) of an inorganic acid such as sulfuric, hydrochloride or phosphoric acid which is effective as a catalyst, and an amount of an organic solvent, miscible with water, sufficient to dissolve the aldehyde. Methanol, ethanol or diethylene glycol may be used. Aqueous methanol solutions containing 30-40% methanol have been found to be particularly satisfactory. Alternately, the aldehyde may be emulsified with a surface active agent. The treatment can be carried out at 3095 C. (preferably at 60-80 C.). The reaction time varies from several minutes to several hours, depending on the other operating conditions. The reaction velocity will rise with increase of catalyst concentration, aldehyde concentration and reaction temperature. Good elastic properties will be obtained at an acetalization degree of 5% up to 50% (preferably 25-30%). The bath may also contain conventional salts to prevent excessive swelling of the polyvinyl alcohol bodies. The salts will be, in general, a salt or a mixture of salts of the acid used.

In the second step of the process the fiber which has already been acetalized with the cyano-substituted aldehyde is heated in an aqueous solution of hydroxylamine or a salt thereof. An organic solvent miscible with water may be added. Improved results may be obtained when a base such as an alkali metal hydroxide or carbonate is added to the bath. Suitable concentrations of metal salts, such as sodium sulfate, may also be added. The bath temperature is generally maintained at about 60-80 C. The reaction time varies according to the circumstances. Usually 2-3 hours is sufficient.

The term polyvinyl alcohol as used in the specification and claims is to be understood to refer not only to polyvinyl alcohol proper but also to its copolymers with other polymerizable compounds, such as ethylene, maleic anhydride, acrylonitrile and the like, provided such copolymers contain at least 80% by weight of polyvinyl alcohol. Such copolymers are known in the art and are .used for the preparation of the same articles, particularly fibers, in the same way as polyvinyl alcohol.

Polyvinyl alcohol fibers which are treated in accordance with this invention are prepared in accordance with known techniques. A preferred method of preparing .the fibers is described in copending application Serial Number 336,166, filed February 10, 1953, now Patent No. 2,988,802, of Tonomari et al.

The following illustrative examples are given to show our novel method and are not intended to limit the invention in any way. All figures are given by weight.

Example 1 A polyvinyl alcohol fiber obtained by a conventional wet spinning process was subjected to heat treatment in air at 235 C. for 3 minutes at constant length. The fiber was then treated with a bath consisting of an aqueous solution of 3.2% of cyanobenzaldehyde, 4.85% 'of sulfuric acid and 39% methanol, in the weight ratio of one part fiber to 50 parts bath, at 60 C. for 4 hours. The fiber thus obtained showed a weight increase due to acetalization of the fiber corresponding to about 26% degree of acetalization of the hydroxyl groups in the polyvinyl alcohol.

This fiber was then treated with a bath consisting of a water-methanol mixture having equal parts of water and methanol which contained 8.5% of hydroxylamine and 6.4% of'sodium carbonate in the weight ratio of one part fiber to 70 parts of bath. When this fiber was dyed at 80 C. for one hour by the conventional dyeing method, using 4% of the acid dyestuff, Acid Brilliant Scarlet 3R, most of the dyestuff was absorbed on the fiber. Fiber which was not treated with hydroxylamine was not dyed at all under the same dyeing conditions.

Elastic recovery of the hydroxylamine treated fiber was 80% after 3% elongation. Therefore, the elasticity did not deteriorate to any appreciable extent as a result of the hydroxylamine treatment.

Example 2 A polyvinyl alcohol fiber obtained by a conventional wet spinning process was subjected to heat treatment in air at 235 C. for 3 minutes at constant length, as in Example 1. The fiber was then treated with an aqueous solution containing 5% m-cyanobenzaldehyde, 8% sulfuric acid and 40% methanol at C. for 2 hours. The fiber thus obtained showed a weight increase due to acetalization of the fiber corresponding to about 27.2% degree of acetalization of the hydroxyl groups in the polyvinyl alcohol. This fiber showed good elasticity, the elastic recovery being 83% at 3% elongation. However, it had no affinity toward either acid or direct dyestuffs.

This fiber was then treated with an aqueous solution containing 10% of hydroxylamine sulfate, 15% of sodi' um sulfate and a suitable amount of sodium carbonate at C. for 2 hours. When this fiber was dyed with the same dyestuff and under the same conditions as the fiber in Example 1, most of the dyestuff was absorbed. The elastic recovery was 82% at 3% elongation.

Example 3 A dry spun polyvinyl alcohol fiber was roller-stretched 500% for one second in air at 210 C. and then contracted 20% for 0.5 seconds in air at 220 C. The fiber was then treated with an aqueous solution containing 3% of 2-fi-cyanoethylbenzaldehyde, 5% sulfuric acid and 33% methanol at 60 C. for one hour. The fiber thus obtained showed a weight increase due to acetalization of the fiber corresponding to about 24% degree of acetalization.

This fiber was treated with an aqueous solution containing 5% hydroxylamine for 3 hours at 70 C. When the resulting fiber was dyed with the same dyestuff and under the same conditions as in Example 1, most of the dyestuff was absorbed. The fiber showed superior elasticity, the elastic recovery being 78% at 3% elongation.

Example 4 .furic acid and 40% methanol at 70 C. for one hour..

The fiber thus obtained showed a total weight increase due to acetalization of the fiber corresponding to about "28.5% degree of acetalization of which the acetalization by means of 4-cyano-1,2,5,6-tetrahydrobenzaldehyde ac counted for 10.2%.

This fiber was then treated with an aqueous solution containing 8% hydroxylamine and a suitable amount of sodium carbonate at 70 C. for 3 hours. When the fiber thus obtained was dyed with the same dyestuff and under the same conditions as in Example 1 most of the dyestuff' -was absorbed. The fiber showed good elasticity, the elastic recovered being 81% at 3% elongation.

vWe claim:

70 fibers characterized by the combination of good dyeabil- 1. A method :of preparing improved polyvinyl alcohol ity and elasticity which comprises acetalizing polyvinyl alcohol fibers wherein the polyvinyl alcohol content is at least 80% with a cyanoaldehyde selected from the group consisting of carbocyclic aromatic monoaldehydes con,-

taining at most 10 carbon atoms in the aromatic nucleus and nuclear hydrogenated derivatives thereof, said aldehyde being characterized by the fact that the aldehyde group is directly bonded to a carbon atom in the nucleus, said aldehyde containing a cyano group as a substituent, to a degree of acetalization of about 5 to 50%, and then treating at a temperature of from about 60 to about 80 C. for from about two to about three hours the acetalized fibers with hydroxylam-ine.

2. A method according to claim 1 wherein the aldehyde is a cyanobenzaldehyde.

3. A method according to claim 1 wherein the aldehyde is Z-(B-cyanoethyl)benzaldehyde.

dyeability and elasticity claim 1.

prepared by the method of References Cited in the file of this patent UNITED STATES PATENTS Kaupin May 14, 1957 FOREIGN PATENTS Great Britain Dec. 23, 1953 

1. A METHOD OF PREPARING IMPROVED POLYVINYL ALCOHOL FIBERS CHARACTERIZED BY THE COMBINATION OF GOOD DYEABILITY AND ELASTICITY WHICH COMPRISES ACETALIZING POLYVINYL ALCOHOL FIBERS WHEREIN THE POLYVINYL ALCOHOL CONTENT IS AT LEAST 80% WITH A CYANOALDEHYDE SELECTED FROM THE GROUP CONSISTING OF CARBOCYCLIC AROMATIC MONOALDEHYDES CONTAINING AT MOST 10 CARBON ATOMS IN THE AROMATIC NUCLEUS AND NUCLEAR HYDROGENATED DERIVATIVES THEREOF, SAID ALDEHYDE BEING CHARACTERIZED BY THE FACT THAT THE ALDEHYDE GROUP IS DIRECTLY BONDED TO A CARBON ATOM IN THE NUCLEUS, SAID ALDEHYDE CONTAINING A CYANO GROUP AS A SUBSTITUENT, TO A DEGREE OF ACETALIZATION OF ABOUT 5 TO 50%, AND THEN TREATING AT A TEMPERATURE OF FROM ABOUT 60 TO ABOUT 80* C. FOR FROM ABOUT TWO TO ABOUT THREE HOURS THE ACETALIZED FIBERS WITH HYDROXYLAMINE. 